ABSTRACT HIV-1, the predominant cause of AIDS in humans, is unable to replicate in most non-human species. Therefore, the most practical animal model of human AIDS consists of infection of macaques with SIVMAC or chimeras derived from SIVMAC. However, the usefulness of these models is limited by the fact that HIV-1 and SIVMAC are distinct viruses. Based on an understanding of species-specific restriction factors, we have generated simian tropic HIV (stHIV) variants that are almost entirely derived from HIV-1 but can replicate in pigtailed macaques. During the last funding cycle, we have used animal adaptation to develop stHIV isolates that cause AIDS in pigtail macaques. Additionally, we have studied the effects of known restriction factors on stHIV replication and unveiled the activity of novel, as yet unidentified, inhibitors that are induced by IFN? and limit lentiviral replication in a species-specific manner in primary cells. The aims of this proposal are to further develop stHIV by deriving novel viral clones that are consistently pathogenic in immunologically intact animals. We will also derive stHIV variants based on HIV-1 strains circulating in humans and ultimately variants for mucosal transmissions. To achieve these aims our studies will include a detailed characterization of viral RNA splicing and functional characterization of in vivo-adapted viral proteins. Additionally, we will generate an stHIV variant where 100% of the sequence is derived from HIV-1 strains by engineering an HIV-1 Vif proteins that can counteract a major species-specific barrier to virus replication: macaque APOBEC3 proteins. Finally, we aim to identify novel IFN?-induced inhibitors that limit stHIV replication in macaque cells and generate stHIV variants that can overcome them. Our preliminary data suggest that these goals are feasible and will lead to the successful development of stHIV variants with the desired properties, an advance that has the potential to transform non-human primate models for HIV-1 drug and vaccine development.